1. Field of the Invention
The present invention relates to a webbing retractor which can impede pulling-out of a webbing at a time when a vehicle rapidly decelerates or the like, and in particular, to a webbing retractor which, after impeding pulling-out of a webbing, enables the webbing to be pulled out again.
2. Description of the Related Art
Generally, in a webbing retractor, a webbing is wound in a roll form on a hollow cylindrical spool (take-up shaft) supported at a frame which is formed in a substantial U-shape as seen in plan view and which is fixed to a vehicle. Usually, the webbing can be freely taken-up or pulled-out due to the spool rotating freely. Further, in the webbing retractor, a WSIR (webbing sensitive inertia reel) or a VSIR (vehicle sensitive inertia reel) is utilized in order to impede pulling-out of the webbing when a rapid deceleration of the vehicle or a rapid pulling-out of the webbing is sensed.
Hereinafter, a conventional webbing retractor equipped with a WSIR and a VSIR will be described on the basis of FIGS. 12A and 12B.
In FIGS. 12A and 12B, a webbing retractor 100 is shown in a side view seen from a rotational axis direction of a spool 102. The webbing retractor 100 is formed to include the spool 102; a lock plate 104 which is supported at the spool 102 so as to be freely swingable and which can mesh with ratchet teeth 106 provided at a frame (not shown); a V gear 108 which is provided coaxially with the spool 102, and when relative rotation with respect to the spool 102 arises, the V gear 108 guides the lock plate 104 to a position at which engagement with the ratchet teeth 106 ismpossible; a W sensor portion 110 which forms the WSIR; and a V sensor portion 120 which forms the VSIR.
In this webbing retractor 100, usually, the spool 102 and the V gear 108 rotate integrally. Thus, the webbing can be freely taken-up and pulled-out (the state shown in FIG. 12A) without the lock plate 104 engaging the ratchet teeth 106.
On the other hand, when the webbing is pulled-out rapidly, an inertia plate 116 of the W sensor portion 110 cannot follow the rotation of the V gear 108 (the spool 102) in the webbing pull-out direction (direction A in FIGS. 12A and 12B), and an inertial delay arises. As a result, relative rotation in the webbing take-up direction arises between the inertia plate 116 and the V gear 108. A pawl 112 which abuts the inertia plate 116 is swung in the webbing take-up direction and engages with internal teeth 118 fixed to the frame, and rotation of the V gear 108 in the webbing pull-out direction is impeded (the state shown in FIG. 12B).
When the rotation of the V gear 108 in the webbing pull-out direction is impeded, relative rotation is generated between the V gear 108 and the spool 102 which continues to rotate along with the pulling-out of the webbing. As a result, the lock plate 104, which has a guide pin 104a which is inserted into a guide hole 108a formed in the V gear 108, does not follow the rotation of the spool 102, and is guided by the guide hole 108a via the guide pin 104a, and reaches a position at which engagement with the ratchet tooth 106 is possible (a position at which the lock plate 104 and the tooth tip of the ratchet tooth 106 engage). The lock plate 104, which has been guided to the position at which engagement with the ratchet tooth 106 is possible, is guided to the tooth bottom of the ratchet tooth 106 by the configuration of the ratchet tooth 106, and is set in a locked state. In other words, the lock plate 104 is self-locked, and rotation of the spool 102 in the webbing pull-out direction is impeded.
At the time of this self-locking, the lock plate 104 moves toward the tooth bottom of the ratchet tooth 106 (i.e., toward the left in FIGS. 12A and 12B). Accompanying this movement of the lock plate 104, the guide pin 104a pushes the guide hole 108a side wall of the V gear 108 toward the left in FIG. 12, and due to this pushing moment, the V gear 108 rotates in the webbing take-up direction (direction B in FIGS. 12A and 12B). When the V gear 108 rotates by a predetermined amount in direction B, the engagement of the pawl 112 and the internal tooth 118 is cancelled. The pawl 112, which is urged to swing in direction A by being connected to one end of a spring 114 whose other end is fixed to the V gear 108, returns to its original position. In other words, the operation of the W sensor portion 110 is cancelled.
In this way, in the process in which the pulling-out of the webbing is impeded, operation of the W sensor portion 110 is cancelled. As a result, thereafter, pulling-out of the webbing is again possible. Note that, when the vehicle rapidly decelerates, tension of a predetermined value or more is applied to the webbing. Thus, while this tension is being applied, the state in which the lock plate 104 is engaged with the ratchet tooth 106 is maintained.
However, with the above-described conventional webbing retractor 100, due to the guide pin 104a of the lock plate 104 pushing the side wall of the guide hole 108a of the V gear 108, the V gear 108 is reversely rotated in the webbing take-up direction (direction B in FIGS. 12A and 12B), and the locking of the W sensor portion 110 is thereby cancelled. Thus, it is difficult to control the reverse rotation angle of the V gear.
Namely, if the reverse rotation angle of the V gear is too small, the amount of rotation of the V gear 108 in the webbing take-up direction is insufficient, and the locking of the W sensor portion 110 cannot be cancelled. On the other hand, if the reverse rotation angle of the V gear is too large, the pawl 112 engages with the next waiting internal tooth 118 and the locked state is maintained. Accordingly, accurate control of the V gear reverse rotation angle is required, and to this end, management of the dimensions of the guide hole 108a and management of the dimensions of the lock plate 104 and the like must be strictly carried out.
In view of the aforementioned, an object of the present invention is to provide a webbing retractor in which a webbing pull-out impeded state can be reliably cancelled, and in which control of a V gear reverse rotation angle is made easy.
In order to achieve the above object, a webbing retractor relating to the present invention comprises: a take-up shaft for taking-up, in roll form, a webbing for restraining a vehicle occupant; a frame which is fixed to a vehicle, and which rotatably supports both end portions of the take-up shaft, and at which a lock tooth is formed in a surface intersecting an end portion of the take-up shaft; a lock plate which is provided at at least one end portion side of the take-up shaft, and which is movable between a position of engagement with the lock tooth and a position of non-engagement with the lock tooth, and due to the lock plate engaging with the lock tooth, the lock plate impedes rotation of the take-up shaft in a webbing pull-out direction; a lock wheel provided coaxially with the take-up shaft at one end portion side of the take-up shaft, the lock wheel usually rotating integrally with the take-up shaft and holding the lock plate at the position of non-engagement, and when relative rotation arises between the lock wheel and the take-up shaft, the lock wheel moves the lock plate to the position of engagement; and a lock operation device having a pawl which is swingably supported and an engagement tooth which can engage with the pawl, the pawl usually being held at a position of non-engagement with the engagement tooth, and in a predetermined case, due to the pawl swinging and engaging with the engagement tooth, rotation of the lock wheel in the webbing pull-out direction is impeded, and due to the lock wheel being rotated in a webbing take-up direction, an engaged state of the pawl and the engagement tooth is cancelled, wherein a guide pin which projects toward the lock wheel is provided at the lock plate, and a guide hole is provided at the lock wheel, the guide pin being inserted into the guide hole, and the guide hole moving the lock plate from the position of engagement to the position of non-engagement or from the position of non-engagement to the position of engagement, and the guide hole is formed to include a first hole portion which holds the lock plate at the position of non-engagement via the guide pin, a second hole portion which communicates with the first hole portion and which, by receiving pushing force from the guide pin, makes the lock wheel rotate reversely in the webbing take-up direction, and a third hole portion which communicates with the second hole portion and which releases pushing force, of a predetermined value or more, of the guide pin which pushing force contributes to reverse rotation of the lock wheel.
In accordance with the present invention, usually, the pawl of the lock operation device is held at the non-engagement position. Thus, rotation of the lock wheel in the webbing pull-out direction is not impeded. As a result, the lock wheel rotates integrally with the take-up shaft, and the webbing is freely both pulled-out from and taken-up onto the take-up shaft. At this time, relative rotation does not arise between the take-up shaft and the lock wheel, and the guide pin of the lock plate is held in the first hole portion of the guide hole formed in the lock wheel.
On the other hand, in a predetermined case such as when the webbing is pulled-out rapidly, the lock operation device is operated. When the lock operation device operates, the pawl engages with the engagement tooth, and rotation of the lock wheel in the webbing pull-out direction is impeded. When rotation of the lock wheel in the webbing pull-out direction is impeded, relative rotation between the take-up shaft and the lock wheel arises, and the lock plate is engaged with the lock tooth of the frame (namely, the lock plate and the lock tooth are self-locked). In this way, rotation of the take-up shaft in the webbing pull-out direction is impeded.
As described above, at the time when the lock plate engages with the lock tooth of the frame, the guide pin of the lock plate passes through the second hole portion of the guide hole formed in the lock wheel. At this time, the wall surface of the second hole portion receives the pushing force from the guide pin, and the lock wheel is rotated in the webbing take-up direction. When the lock wheel rotates in the webbing take-up direction, the engaged state of the pawl and the engagement tooth at the lock operation device is cancelled.
Here, in the present invention, the third hole portion, which communicates with the second hole portion, is provided. Thus, in a case in which a pushing force of a predetermined value or greater is applied from the guide pin, the guide pin enters into the third hole portion, and the pushing force can thereby be avoided. Accordingly, the reverse rotation angle of the lock wheel can be prevented from becoming larger than needed. In other words, in accordance with the present invention, at the second hole portion, the reverse rotation angle of the lock wheel can be set to be slightly larger than the target value, so that the reverse rotation angle of the lock wheel does not become too small. If a reverse rotation angle which is greater is about to be applied to the lock wheel, the pushing force which contributes to that reverse rotation angle can be absorbed (cancelled) at the third hole portion. As a result, in accordance with the present invention, a situation can be prevented in which the reverse rotation angle of the lock wheel is too small and the lock operation device is not cancelled. Further, a situation can be prevented in which the reverse rotation angle of the lock wheel is too large, and the pawl engages with the next waiting engagement tooth.